Field of the Invention
This invention relates to the field of battery protection and particularly to a battery structure with a built-in fuse holder to place a fuse directly in series between the current-generating cell and one of the battery terminals.
It is well known that batteries of a certain size, and particularly, but not exclusively, those used in riding toys of a type large enough to be ridden by small children, can discharge through a very low-impedance circuit at a rate fast enough to generate a dangerous amount of heat capable of starting fires and burning anyone who touches the circuit components. As a result, it is common practice to connect a fuse in series with the battery to break the circuit if the current is excessive. While a fuse can protect the battery against a short-circuit connection beyond the fuse, it does not provide any protection against a short-circuit connection directly across the battery terminals. In fact, some batteries have their terminals at the ends of wires several inches long, and it is possible to create a short-circuit connection from one of those wires to another at a location between the terminals and the main part of the battery structure, if, for example, a metal member that is essentially like a blade cuts across the wires.
It is particularly important to guard against such an eventuality in childrens' toys. The children cannot be expected to understand the danger if such a short-circuit connection occurs, and furthermore, the batteries used in childrens' riding toys must be capable of furnishing a relatively high current of several amperes in normal usage so that the possible current under short-circuit conditions will be quite dangerously high.
Batteries are also subject to being heated more slowly, for example, by a overload that draws an excessive current but not as much as a short-circuit connection. It is common to provide thermal protection for batteries by putting a thermal shutdown device, which is similar to a thermostat in series with the battery terminals and inside the battery case. Excessive heat in the case causes bimetallic elements in the thermal shutdown device to bend, thereby open contacts in series with the terminals and rendering the battery inoperative until it cools down.
While thermal shutdown devices interrupt the flow of current from the battery, they do not operate with the almost instantaneous speed of fuses, and since they are self-resetting, they do not provide the permanent protection that fuses do. A thermally protected battery that remains connected to an overload would be repeatedly connected to and disconnected from the overload until the charge generated or stored in the battery was dissipated. The fuse in a fuse-protected circuit would blow on the first overload and the circuit would remain open thereafter until the fuse was replaced, at which time, presumably, the element causing the overload would be removed.
Because a thermal shutdown device is self-resetting, it can be built in as a permanent part of the battery. A fuse, on the other hand, must be replaceable, which means that some means must be provided to insert the fuse into a holder that is part of the battery structure, and as to the holder and its terminals, must not include openings that destroy the integrity of the battery case, or enclosure. This is especially true in the case of gel-type storage batteries used in toy vehicles large enough to be ridden by children. It is essential that there be no opening that would permit the electrolyte in the battery case to leak out.
It has been proposed in the past to incorporate a fuse within the battery case and electrically connected in series with one of the cell terminals within the case so that the fuse is electrically between that cell terminal and one of the battery terminals to which electrical circuits can be connected. U.S. Pat. No. 3,937,636 to Slautterback, issued Feb. 10, 1976, discloses a fuse-protected battery, but the fuse and connections to each end of it are covered only by a hinged plate. If opened, this plate uncovers the connection from the fuse to the cell terminal, such exposure of that connection is very undesirable in that it provides undesirably easy access to the cell terminal and would make it possible to place a short circuit between cell terminals without forcing the short-circuit current to flow through, and immediately blow, the fuse.
U.S. Pat. Nos. 4,217,400 and 4,315,364 to Leffingwell, issued Aug. 12, 1980 and Feb. 16, 1982, respectively, show a fused battery pack in which the fuse is within the pack and is therefore not directly accessible from outside the pack, as required for ease of replacement. When the part of Leffingwell's enclosure that covers the fuse is opened, the cell terminals are directly accessible.